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12 V. Neg Ground Alternator wiring. AGAIN

stevieb49829

stevieb49829

Well-known Member
Location
Spirit Lake, Idaho
I read everything I could find on this topic, and then I wired my 12V 10SI alternator #1 terminal through a diode, to the + side of my coil, because it was close to the alternator, and is an ignition switched circuit. It works flawlessly, charging at 14.6 volts instantly. Is there a hidden problem doing it this way instead of a dedicated circuit from the ignition switch? The coil feed wire is at least a 16 ga. braided copper. Steve
 
That will work fine, you did not tell us what machine you are doing this on. If it has a resistor or a resistance style lead wire it will not have a full 12 volts at the coil. Apparently it is enough to excite the regulator. Only rare occasion may be if the battery is run down and you crank, roll or pull start your tractor it may not have enough voltage through the resistance feed to energize the alternator. I do not know what the required voltage for that is. However, I would like to say if you have enough to fire the coil it will probably excite the regulator. If you do have a resistor block at the coil move the wire to your diode to the opposite side of the block from where the coil connects.
 
No resistor in the way of the full 12V getting to the coil. MH 101 Jr., converted to 12V negative ground by the PO. I just rewired the really shoddy old wiring, and installed the diode (they didn't have the alternator wired yet). Also fused the dash and gauge lights, and headlight/back work lights, and an inline 30 amp auto reset breaker in the main supply. I kept the push button start switch, but I considered wiring in a starter solenoid as I did this. Is there an advantage to using a solenoid over the heavy-contact start button? It still works well. steve
 
So hopefully you have a full 12 volt coil on it with 2.5 - 4 ohms of resistance across the low volt terminals. The starter switch is fine in my opinion, just be deliberate when pushing or pulling whatever you do so it engages with a firm pressure on the contacts.
 
The 30 amp breaker might be a little light if the alternator is charging through it and the battery is really low. Otherwise it should be fine. You could wire the alternator directly to the battery cable so it doesn't go through the breaker. It's not good for an alternator to break circuit running or try to bring up a dead battery.

On the starter switch, some have the neutral safety designed through that switch, not sure about yours. But an easy fix if it gives trouble is to add a solenoid, use the original starter switch to energize the solenoid. That takes the load off the contacts and keeps the safety in place (if equipped).
 
Thanks, Steve. I moved my alternator wire to the battery side of the breaker, so it now goes directly to the battery, and not through the breaker. The breaker is now protecting anything that would create a draw, except a direct short in the alternator-to-battery circuit. I suppose I should put a fusible link in that line, too? steve
 
I have 1.5 ohms of resistance across the coil. Is that too little? The hood is on, obstructing my view of the coil, but I'm pretty sure it is a 12 volt coil. Should I pull the hood and make sure? Will it say it's a resistor coil on it? steve
 
never mind, I found my answer: at 1.5 ohms it is likely a 6 volt coil, and would need a resistor to get it up near the 3 ohms I need to save the points. There is no resistor in the system, not even a resistance wire. I know what they look like, and may have one in my box of misc. automotive wires. So I need to add about 1.5 ohms, with either a ballast resistor or a resistance wire?
 
I pulled the hood and it IS a 12 volt coil, but it DOES say use an external resistor. I should have looked and saved you all some time answering my dumb-A questions.
 
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